1. Field of the Invention
The present invention relates to an ultrasonic horn for applying ultrasonic vibrations to multiple objects to be bonded so as to bond them, and to an ultrasonic bonding apparatus using the ultrasonic horn.
2. Description of the Related Art
The following description makes reference to a Patent Reference 1, Japanese Unexamined Patent Application Publication No. 2001-44242, and a Patent Reference 2, Japanese Unexamined Patent Application Publication No. 2001-110850.
Ultrasonic bonding apparatuses are used in the process of flip chip mounting of electronic parts, such as semiconductor devices and piezoelectric devices, on boards.
Patent Reference 1 discloses an ultrasonic bonding apparatus wherein a member to be bonded to a face is subjected to a pressing load and ultrasonic vibrations, so as to be bonded to the face. This ultrasonic bonding apparatus has a vibrator mounted on the tip of a pointed horn, for applying vertical vibrations, which are vibrations in the longitudinal direction of the horn, and a bonding tool positioned at the loop of standing waves of the vertical vibrations of the horn, approximately orthogonal to the direction of vertical vibrations from the horn. A connector with pressing means for applying a pressing load is provided at the approximate center of the horn.
Patent Reference 2 discloses an ultrasonic bonding apparatus wherein a generally T-shaped horn is turned sideways, a vibrator is attached to one end of the sidebar portion thereof, and the vertical bar is formed in a cylindrical shape through which a holding member is passed, and pressing means for applying the pressing load is connected to the tip of this holding member. In this case, the means for applying the pressing load (i.e., the holding member) and the means for applying ultrasonic waves (i.e., the horn) are configured as separate members, and have separate functions.
However, with the arrangement disclosed in Patent Reference 1, the bonding tool which is subjected to vertical vibrations of the horn flexes and vibrates, so the tip portion thereof swings like a pendulum, and ultrasonic vibrations cannot be applied to the bonding face in a constant direction. Accordingly, there are differences in vibration components between the center and edge portions of the bonding portion, resulting in irregularities in the bonding state depending on the part. Consequently, the bonding is not uniform, so bonding quality is poor, and there is also the problem that additional damage to the bonded members may result in cracking, splitting, chipping, and so forth.
On the other hand, with the arrangement disclosed in Patent Reference 2, the holding member for applying the pressing load to the bonding portion and the cylindrical portion of the horn for applying the ultrasonic vibrations are not completely separate but rather in contact, so vibrations are also applied to the holding member. Accordingly, the vibrations applied to the bonding portion have multiple modes, so vibrations suitable for bonding cannot be applied. Also, the tip of the T-shaped horn in contact with the bonding portion flexes and vibrates, so ultrasonic vibrations cannot be applied to the bonding face in a constant direction. This causes a problem of poor bonding quality at the bonding portion.